Getting enum associated with int value

Question

Previously, I had my LegNo enums defined simply as:

NO_LEG, LEG_ONE, LEG_TWO 

and by calling return LegNo.values()[i];, I was able to get the value associated with each enum.

But now I've decided I want the LegNo enum NO_LEG to be the int -1 instead of 0 so I decided to use a private constructor to initialise and set its int value

NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);  private LegNo(final int leg) { legNo = leg; } 

the only thing now is that because I'm doing it this way the values() method will not work for the NO_LEG enum. How do I get the enum associated with the int? Is there any efficient way of doing this other than using a case switch statement or an if-elseif-elseif

I can see a lot of SO questions to do with getting the int value from the enum, but I'm after the reverse.

Answer 1

EDIT August 2018

Today I would implement this as follows

public enum LegNo {     NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);      private final int value;      LegNo(int value) {         this.value = value;     }      public static Optional<LegNo> valueOf(int value) {         return Arrays.stream(values())             .filter(legNo -> legNo.value == value)             .findFirst();     } } 

---

You'll have to maintain a mapping inside the enum.

public enum LegNo {     NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);      private int legNo;      private static Map<Integer, LegNo> map = new HashMap<Integer, LegNo>();      static {         for (LegNo legEnum : LegNo.values()) {             map.put(legEnum.legNo, legEnum);         }     }      private LegNo(final int leg) { legNo = leg; }      public static LegNo valueOf(int legNo) {         return map.get(legNo);     } } 

The static block will be invoked only once, so there is practically no performance issue here.

EDIT: Renamed the method to valueOf as it is more inline with other Java classes.

Answer 2

You could also include a static method in the enum that iterates through all members and returns the correct one.

public enum LegNo {    NO_LEG(-1),    LEG_ONE(1),    LEG_TWO(2);     private int legIndex;     private LegNo(int legIndex) { this.legIndex = legIndex; }     public static LegNo getLeg(int legIndex) {       for (LegNo l : LegNo.values()) {           if (l.legIndex == legIndex) return l;       }       throw new IllegalArgumentException("Leg not found. Amputated?");    } } 

Now, if you want to get an Enum value by the integer, you just use:

int myLegIndex = 1; //expected : LEG_ONE LegNo myLeg = LegNo.getLeg(myLegIndex);